This invention relates to improvements in video image creation systems.
In the system shown in FIG. 1 and described in U.S. Pat. No. 4,514,818 (U.S. Pat. No. 4,518,818) a video image may be created which resembles closely a picture created using conventional materials. The operator may choose a colour and notional implement by using a keyboard 1 and then by `drawing` on a touch tablet 2 with a stylus an image is caused to appear on the TV colour monitor display 8. Choosing an implement and colour causes digital signals representing a luminance or chrominance distribution for a group of points adjacent to the designated picture points to be loaded into RAM 4 and causes digital signals representing three components of the chosen colour (at some reference luminance level) to be loaded into RAM 5. The three colour components in this example are Y, I and Q and the respective RAMs are denoted by the suffices A, B and C. Each RAM has a number of storage locations representing a sequence of picture points sufficient in number to represent the maximum area of distribution of the implements which can be chosen.
When a picture point is designated on the touch tablet by contact of the stylus, the address generator 9 derives signals representing the addresses of a square of storage locations in three frame stores 7A, 7B and 7C, provided respectively for the three colour components Y, I and Q. The size of the square corresponds to the sequence of locations in the RAMs 4 and 5, and the addresses generated by the address generator 9 are such as to locate the square at a position in the frame, determined from the co-ordinates of the point touched by the stylus.
For example, the address generator 9 and computer 3 may translate the co-ordinates to a corner of the patch. As each location in the square is addressed in the frame store 7A, 7B and 7C the corresponding locations are addressed in the RAM 4 and 5. For each point touched by the stylus there is read previously stored video signals for the respective square of storage locations and at the same time there is read the colour component signals from RAM 5A, 5B and 5C, and the distribution signals from RAM 4. The outputs are processed in processor 6A, 6B and 6C on a picture point by picture point basis with the digital signal information stored in the frame store 7 for each respective picture point.
In each processor the respective colour component signal is multiplied by the distribution signal read from the RAM 4 and the product combined in a predetermined way with the corresponding video signal from the frame stores 7A, 7B and 7C to produce a new video signal which is then written into the respective location in the frame store.
In this way each new picture point designated by the stylus is made up of a portion of the stored, as well as the incoming video information. Each distribution is for a patch of picture points adjacent the point designated by the touch tablet and stylus. The image is displayed on display 8.
The system can be set so that other information may be introduced to vary the picture point video signals. For example the pressure of the stylus on the touch tablet may be taken into account or the length of time the stylus is held over a point by providing that signal representing the pressure or length of time are used as multiplying factors for the colour component signals in RAMs 5. A facility for `blurring` may also be available to simulate the effect of a rubber.
For a variety of practical considerations, such systems are usually limited to producing a video picture of broadcast television standard but there are many purposes for which a picture of much higher resolution would be desirable.